Intensifying and fluorescent screen



April 13, 1937. J, EGGERT ET AL 2,076,984

INTENSIFYING AND FLURESCENT SCREEN Filed March 8, 1934 In ven fors @dwf Patented Apr.l 13, A1937 UNITED s'rAT-Es Y 2,076,984 l mTENSIFYING AND FLUonEscEN'r SCREEN Jaim Eggert, Leipzig-Gallus, and 'Fritz Luft,

Leipzig, Germany,v assgnors to Agfa-Ansco Corporation, Binghamton, N. Y., a. corpora.-

tion of New York Application March 8,

4 Claims.

Our `present invention relates to an intensifying or fluorescent screen for X-ray work.

One of its objects is an improved screen of this kind. Further objects will be seen from the de- 5 tailed specification following hereafter.

Many intensifying and uorescent screens for `use-in X-raywo'rk have'the drawback to show phosphorescence, thatv is to say, the screens not i, only emit the desired uorescent radiation during the diagnostic exposure, but also produce after eiiposure a phosphorescent light, at the places previously struck bythe `X-rays so that on the screens the successively produced phosphorescent and uorescent pictures become mixed, a fact which may render diilicult the interpretation of the inspected or photographed. picture. As known,- it is very difficult to free the luminescent substances used in the manufacture of intensifying screens and fluorescent screens for X-ray o work from substances that phosphoresce when struck by X-rays.

This phosphorescent light frequently has a color different from that of the fluorescent light. By the invention the detrimental effect caused by the phosphorescent substances contained in y the fluorescent layer may be eliminated by coating the intensifying screen or the fluorescent screen with a filter layer which transmits the uorescent light completely` or in greater part,'lbut absorbsl the phosphorescent rays. By this expedient the manufacture of intensifying and fluorescent screens for X-ray work is considerably cheapened and improved, because on the one hand the In Germany March 15, .1933

1934, serial No. 714,729

tessuto instead of being incorporated ina special lter layer. v

Furthermore, substances are known, such as zinc sulfide and suldes of the alkaline earths, which fluoresce and phosphoresce whenV struck by X-rays or by daylight. If such substances are used for the manufacture of intensifying screens, these screens must, of course, always be protected from daylight, thus causing much trouble in X- ray Work.

Now, according to Stokes law, these luminescent rays always have -a greater wave length than the exciting primary rays. By'providing fluorescent screens with a filter (in the Way above referred to, i. e. applying a lterlayer by casting or dyeing the layer throughout its thickness) which absorbs only the exciting light, and transmits the luminescent rays'completely or in greater part, the risk that such a screen be excited in daylight is greatly diminished, without the ex citability by X-rays being'reduced or the emission of the fluorescent rays being materially hindered. With a screen protected in this manner, therefore, X-ray work may be done almost irrespective of any previous exposure to daylight.

In the following table there are given some materials which are used for manufacturing in. tensifying or fluorescent screens and materials which they may containas impurity. There is furthermore indicated the uorescent and phosphorescent light emanated by these materials vand the lter Ydye to be used for absorbing the phosphorescent light,

asv

Color.l of Color of phos- Mam consument Imputy fluorescence phorescenee Filter dye ZnS activated with Mn Dark blue-.- Orange Toluidine blue (ci. Schultz Farbstoitabellen Ag. t 7th edition No. 1041) or Crystal violet (hexamethylpararosaniline). A 40 ZnS activated with Cu Darkblue.-. Green Rose bengale ci. Schultz Farbstoiftabellen g. 7th edition N o. 889). ZnS activated with Mn Orange yel- 4Green Orange 2 (ci. Schultz Farbstotabelien 7th Cd. low. edition N 0.189). CaWO4 ZnS ac- Blue Green- .-e--.- Rose behgale (ci. Schultz Farbstoiltabellen tivated 7th edition No. 889).

w i t h ncomplicated process of removing the phosphoresy The following examples illustrate the invention:

Example 1.-An intensifying screen for X-ray work consists of a support, for instance stiff paper, and a uorescent layer, containing as a fluorescent substance, zinc sulfide activated with silver. This layer is coated'with another layer containing as a lter dyestuff hexamethylpararosaniline in gelatin asa'binding agent. If the zinc sulde'activated with silver and fluorescing in a blue color, contains as usual traces of copper, the screen will phosphoresce in a green light, e

which is absorbed by the filter layer containing hexamethylpararosaniline. The blue fluorescent light penetrates'the filter layer unweakened.

Example 2.-An intensifying screencontaining as an active substance zinc sulde activated with copper is coated. with a green filter layer of gelatin dyed withy Tartrazine (cf. 'Schultz Farbstofftabellen 7th 'edition No. .737), and Patent Blue (cf. Schultz Farbstoitabellen` 7th edition No. 826). This filter layer prevents the screen from being excited by daylight by absorbing the blue rays exciting phosphorescence. On the contrary, X-rays which are not absorbed by such a filter excite a fluorescent radiation. The yellowishgreen uorescent light produced is transmitted by the filter layer.

Our invention is illustrated in the accompanying drawing in which Fig. 1 shows a modification in which the layer containing the iluorescent material is provided with a'filter layer for absorbing phosphorescentlightand Fig. 2 shows a modification in which 'the layer containing the iiuorescent material is colored throughout by a f dye absorbing phosphorescent light.

What We claim is:

1. An intensifying jor fluorescent screen for X- ray work which comprises a layercontaining a fluorescent material and a filter layer containing a dye 'permeable for the fluorescent light produced on excitationA of said uorescent material and absorbing the phosphorescent light.

2. An intensifying or fluorescent screen for X- ray work which comprises in its active layers a uorescent material and a dye permeable vto uorescent light produced on excitation of said fluorescent material and absorbing the phosphorescent light.

3. An intensifying or fluorescent screen .for X- ray Workwhich comprises uniformly distributed in a binding agent a fluorescent material and a dye permeable to uorescent light produced an excitation of said fluorescent material and absorbing the phosphorescent light.

4. An intensifying or uorescent screen for X- ray work which comprises, a layer containing zinc sulde activated with silver and coated' on this layer with a layer of, gelatin dyed with hexamethylpararosaniline. I

' JOHN ,EGGERTA FRITZ LUFI'. 

